The present invention relates to an antenna system according to the generic part of claim 1.
It is generally known to receive radiofrequency signals with frequency values above hundreds Megahertz, corresponding to wavelengths of less than about 50 centimeters, with the aid of a parabolic reflector and a feeder located at the focal point of said reflector.
It is further known to use other focussing means as the parabolic reflector, e.g. a dielectric lens. Antenna systems using dielectric lenses, such as a Luneburg-type or a homogeneous-type lens, are known for example from the international publication WO 92/13373, where such a lens is used in conjunction with a helical antenna.
The known kinds of feeders, such as feeder horns and helical antennas, require waveguides or coaxial lines to lead the received signals to associated electronic means, such as a low noise block (LNB). Such a weveguide-solution is bulky and complicated. As it uses two kinds of technologies, waveguide for the feed and microstrip for the LNB, it is a quite expensive product.
It is further known, e.g. from the article "MICROSTRIP ARRAY FOR RFLECTOR FEED APPLICATIONS", P. S. Hall et al., Conference Proceedings of the 14th European Microwave Conference in Liege, Sep. 10-13, 1984; pages 631-636, to use a small array of conventional microstrip patches as antenna feed for just one polarization and a relatively narrow frequency band width.
It is further known, e.g. from "ANTENNA ENGINEERING HANDBOOK", second edition, R. C. Johnson et al., McGraw-Hill Book Company, 1989; chapter 8, to use slot antennas. Such antennas may have a rectangular, an annular shape or the like.
It is an object of the present invention to present an antenna system with concentration means, such as a dielectric lens antenna or a parabolic reflector, and a light weight and compact feed which can be directly integrated with rear-positioned electronical means, such as a low noise block (LNB).
This object is realised by an antenna system according to claim 1. Further developments are given by the sub-claims.
According to the present invention an antenna element for the reception of radiofrequency signals and especially for microwave signals is a slot antenna and is arranged on the same board as electronical means for processing the signals received by the antenna element.
The invention has the advantage, compared to existing microstrip arrays, that there is less pattern disturbance by feeding circuits and that a better integration to the feed is possible by lower dimensions and by saving some components.
It is preferred to give the antenna element the shape of an annular slot. This has the advantages of a good polarization diversity and of a wide frequency bandwidth coverage.
In a development of the invention the slot antenna is etched in the backside of the board used for the rear-positioned electronic means. This backside can be outside of the antenna area e.g. the conductor for ground.